1. Field of the Invention
The present invention relates to an image heating apparatus for heating images on a recording material used in an image-forming apparatus employing an electrophotographic system or an electrostatic recording system. The image heating apparatus may include a fixing device for fixing unfixed images on a recording material and a gloss increaser for increasing the gloss of images by heating the images fixed on the recording material.
2. Description of the Related Art
So-called belt fixing devices using a fixing roller and a pressure belt have been devised (Japanese Patent Laid-Open No. 11-194647 and Japanese Patent Laid-Open No. 5-27622, for example).
Specifically, in the belt fixing device, a recording material carrying unfixed toner images thereon is introduced into a fixing nip between the fixing roller and the pressure belt so as to fix the toner images on the recording material with heat and pressure while the recording material being pinched and conveyed.
In such a belt fixing device, the width of the fixing nip (the length of the fixing nip in the conveying direction of the recording material) can be increased in comparison with that of a conventional roller fixing device using a fixing roller and a pressure roller.
Since the width of the fixing nip of such a belt fixing device can be increased without increasing the diameter of the fixing roller, the thermal capacity can be reduced, enabling the warming-up period to be decreased.
For at least this reason, the application of the belt fixing device to a color image-forming apparatus is particularly advantageous in view of the melting and color mixing of the multi-color toner images formed on the recording material.
In the belt fixing device, the belt shows a tendency to deviate in its width-wise direction (direction perpendicular to the belt rotational direction), so that the belt deviation must be restricted.
In the conventional belt fixing devices mentioned above, a system in that the belt is swung in the width-wise direction by displacing a belt stretching roller has been proposed. According to this system, the belt can be prevented from being buckled and damaged as a result of contacting another member at its end.
However, in the above system, the control cannot respond to the deviation of the belt between when it abuts the fixing roller and when it is separated therefrom, so that the belt may fully deviate.
This may be caused by the fact that the load applied to the belt when the belt is separated from the fixing roller is smaller than that when it abuts the fixing roller so that the rocking speed of the belt is increased.
Thus, by the conventional belt rocking system, the belt may fully deviate and be damaged.